The following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art.
U.S. Pat. No. 4,394,351 to Gast discloses a dual-monolith catalytic converter having upstream and downstream located substrates and a configuration such that the exhaust gas flow is non-uniformly distributed across the upstream frontal areas of each of the substrates and concentrated centrally of such frontal areas. The converter further has a chamber located between said substrates. An air distribution tube having an open end adapted to be connected to the pulsed air supply extends through and across the chamber substantially normal to the exhaust gas flowing between the substrates and terminates with a closed end. The tube within the chamber has a plurality of holes which are sized and spaced along the tube to non-uniformly distribute the pulsed air supply throughout the chamber in a manner to provide a resultant air flow distribution conforming with the non-uniform distribution of exhaust gas. Flow dividers are spaced along the tube and extend substantially parallel to the flow of exhaust gas between the substrates in a manner to partition the chamber into a plurality of discrete channels each open to selected ones of the holes to receive one portion only of the non-uniform distribution of the pulsed air supply and one portion only of the non-uniformly distributed exhaust gas whereby the non-uniform air flow distribution is maintained between the channels while the exhaust gas is flowing between the substrates to prevent the exhaust gas from entering the downstream substrate with an improper mix of pulsed air so that the conversion efficiency of the downstream substrate is maximized.
U.S. Pat. No. 5,578,277 to White et al. discloses a modular catalytic converter and muffler used to purify exhaust from a relatively large diesel engine. The device includes various structural components that are mounted in the exhaust flow path within a housing having an inlet and an outlet. A plate mounted within the housing divides the housing into an inlet chamber and an outlet chamber. A plurality of catalytic converter sub-cans are mounted across the plate between the inlet chamber and the outlet chamber. A flow distributor is mounted within the housing upstream of the catalytic converter sub-cans. The flow distributor divides and directs a portion of the exhaust to each of the catalytic converter sub-cans. Some muffler structure is mounted within the housing between the catalytic converter sub-cans and the outlet in order to attenuate noise in the exhaust.
U.S. Pat. No. 7,210,287 to Bolander et al. discloses a method of reducing exhaust emission from a catalytic converter apparatus of a vehicle, the apparatus including at least one catalytic converter, each of the at least one catalytic converter having a catalyst brick positioned within a predefined length of the vehicle. The method includes directing exhaust to pass more than once through the predefined length through at least one of the at least one catalyst brick. The converter apparatus can accelerate catalyst conversion reactions and thus accelerate converter system light-off.